Modularity is becoming an important feature in the firearm industry. Generally, a modular firearm is a firearm that may be reconfigured with one or more different components to change the operation, function, size and/or shape, and/or capabilities of the firearm. Barrel length and rifling, muzzle type, muzzle brake, flash suppressor, compensator, magazine capacity, butt stock length and type, are examples of commonly adjustable components of a typical modular system. Modular firearms may also provide for multiple caliber configurations, i.e., a user may reconfigure the firearm for use with more than one caliber cartridge.
Modular firearms may be formed of modular components, each of which may be replaced with an identical component for repair and maintenance, or a variant component that provides a change in operation, function or capability, for example. Typically, a modular rifle includes a barrel, a chassis and receiver, a firing mechanism that may include a bolt assembly and a trigger assembly, and a butt stock. Some modular rifles enable a user to reconfigure the firearm for use with different caliber ammunition, such as by replacing caliber-specific barrel, magazine, and bolt assembly components for similar components configured for a different caliber, for example.
The ability to reconfigure a firearm for use with different caliber ammunition is valuable for several reasons. First, certain calibers of ammunition can be very expensive, whereas other calibers may be significantly more affordable. The latter ammunition category may be used in high volume for training purposes, while the former ammunition category may be used in low volume for operational purposes, competition, and the like. A firearm that may be reconfigured for use with either ammunition category allows a user to practice and train with the more affordable ammunition, building repetition knowledge (e.g., muscle memory) and experience with the firearm, and easily transition to using the more expensive ammunition for other purposes. Also, ammunition types are designed for different purposes. As examples, some calibers are designed for long-range anti-personnel or anti-materiel use, other calibers are designed for target shooting, and other calibers are designed for game hunting. Thus, a firearm that may use more than one type or caliber of ammunition may be configured for more than one role or purpose, increasing the range of roles that the firearm may fulfill.
One of the challenges with a modular firearm is providing a reconfiguration process which is not complicated and cumbersome, and does not require extensive, complicated, or unusual tools. Ideally, the reconfiguration process involves a minimum number of parts, and requires few tools (if any) to complete the modification. Also, the reconfiguration process should be as safe as possible. A primary design consideration is the safety of the firearm throughout the entire reconfiguration process. The process itself must allow a user to safely reconfigure the firearm in numerous conditions, including the full range of low-stress environments to highly stressful operational situations. The process must also account for the human error factor, in which a user may not (for myriad reasons) correctly perform the reconfiguration process. For example, a user may fail to include all components during reassembly, or improperly align components. Ideally, the reconfiguration process is a simple and straightforward such that a user either cannot physically complete the process without doing so correctly, or the firearm does not function in a state of an incomplete or incorrect reconfiguration.
These considerations apply to the bolt assembly in a modular firearm. For many multi-caliber modular firearms, the bolt head is specific to the caliber. Thus, to configure the firearm for use with more than one caliber ammunition, one option is to provide a bolt assembly that is specific to each caliber. This option is cumbersome and expensive. Other options employ a removable bolt head that mates with a bolt body and handle, such that only the bolt head need be replaced to reconfigure the firearm for use with a different caliber.
U.S. Pat. No. 8,429,844 to Dextraze et al. (“Dextraze”) describes such a modular bolt assembly with a bolt head that may be removed from the bolt body, for use with a bolt-action rifle. Dextraze teaches varying the bolt head depending on the desired configuration, such as for use with a specific caliber. Dextraze's firing pin assembly may be inserted into a hollow bolt body and bolt head. The bolt head may be locked in position through a locking pin that fits through the bolt body and bolt head, as well as the firing pin assembly fitting into the bolt head.
There is a significant safety concern with bolt assemblies similar to the type described by Dextraze: because the firing pin extends from the striker assembly, the firing pin can be activated in the absence of the bolt head. Engaging the firing mechanism may cause the firing pin to strike the primer, even if the bolt head is not installed. As a consequence, the primer in a cartridge can ignite and the resulting explosive forces release through the open chamber, magazine well, ejector port, etc., causing severe injury to the user and potentially catastrophic damage to the firearm and surroundings. In other words, firing mechanisms such as the mechanism Dextraze discloses may be capable of operating even if the user fails to replace the bolt head during assembly, during reconfiguration, or after maintenance, for instance, and is therefore a significant health and safety risk. Also, an exposed firing pin, such as in the Dextraze mechanism, is easily damaged through handling. Damage to the unprotected end of the firing pin can change the shape and overall firing pin length, which may result in inconsistent primer strikes, possibly resulting in misfire.
What is needed is a self-aligning modular bolt assembly capable of being reconfigured with a caliber-specific bolt head that does not contact the primer if improperly or incompletely assembled.